1. Technical Field of the Invention
The present invention relates generally to a holding furnace for holding metal molten and a method for holding molten metal therewithin, and more particularly to an improved structure of a holding furnace designed to eliminate contaminants contained in molten metal to produce high purity molten metal preparatory to casting and an improved metal holding method using the same.
2. Background Art
FIG. 6 shows a conventional molten metal holding furnace. A furnace body 68 defines therein a reservoir chamber holding molten metal. From an ingot inlet port 62 formed in an upper wall 61 of the furnace body 68, an ingot is supplied into the reservoir chamber, which is, in turn, heated by a heater 63 to produce molten metal. The molten metal is held at a given constant temperature. The level 64 of the molten metal is kept away from the heater 63 so that it is maintained even. Additionally, the level 64 of the molten metal varies once a portion thereof is drawn out of the reservoir chamber, thereby causing an air layer to be formed over the level of the molten metal. An agitator 65 is arranged which stirs the molten metal and ejects through its end inert gas, or so-called bubbling gas for reduction in hydrogen gas generated in the molten metal. The molten metal from which contaminants such as oxide have substantially been removed flows between barriers toward an outlet port along an arrow 67.
In the conventional molten metal holding furnace, the oxide produced from the molten metal is removed manually by a furnace operator. This is quite inconvenient. Additionally, since it is difficult to remove the oxide completely, castings may be contaminated with the oxide, thus resulting in degradation in quality thereof. Further, the heater is so arranged as to produce heat to the molten metal indirectly, thus leading to loss of heat energy.